A known light source has a fluorescent material plate supported by a supporting member. The fluorescent material plate is irradiated with light emitted from a semiconductor laser to obtain white light. If the fluorescent material plate peels off or the fluorescent material plate is detached from the support member due to vibration or shock, there is a risk that the laser light directly travels to the outside. In a vehicular headlamp or the like, a driver of an oncoming vehicle may be irradiated with laser light in this case. To cope with these problems, there are also safety standards for laser products.
As shown in FIG. 3A, it is proposed that a circuit pattern substrate 110 having a window is disposed above a semiconductor laser 105, a fluorescent material plate 111 having a reflective electrode 108 surrounding an irradiation region with laser light having passed through the window of the circuit pattern substrate 110 is disposed on (above) the circuit pattern substrate 110, and the fluorescent material plate 111 is irradiated with the laser light from the semiconductor laser 105 through the opening of the reflective electrode 108. The driving current for the semiconductor laser 105 is supplied from a driving circuit including the reflective electrode 108 on the fluorescent material plate 111 as a part of wiring. When the fluorescent material plate 111 is detached from the circuit pattern substrate 110 due to some reasons, the wiring of the driving circuit is disconnected, so that the operation of the semiconductor laser 105 is stopped (see, for example, Japanese Patent Application Laid-Open No. 2014-165450).
Another known laser lamp unit has a configuration in which light from a laser element is condensed by a lens, and the laser light incident on and transmitted through a fluorescent material and fluorescence by the fluorescent material are combined together to generate white light.
Further proposed is a laser lamp unit of a type in which laser light is scanned by a mirror or the like to selectively irradiate light in accordance with the position of an oncoming vehicle (see, for example, Japanese Patent Application Laid-Open No. 2017-056762).
As shown in FIG. 3B, for example, there has been a proposal for such a lamp unit in which right and left longitudinal centers of a rectangular central portion 121 are coupled to an intermediate portion 123 by torsion bars 122a and 122b, and the upper and lower lateral centers of the intermediate portion 123 are coupled to an outer portion 125 by torsion bars 124a and 124b. Grooves G1a and G1b are formed between the central portion 121 and the intermediate portion 123, and grooves 124a and 124b are formed between the intermediate portion 123 and the outer portion 125. A mirror mechanism capable of scanning the reflected light in the two-dimensional manner is formed by disposing a mirror plane M in the central portion 121 and further providing a drive mechanism such as a piezoelectric element to the torsion bar portions 122 and 124 (see, for example, Japanese Patent Application Laid-Open No. 2005-148459).
In a laser headlight of the type that scans laser light, laser light having a high intensity is scanned over a fluorescent material plate. Since the light emitted from the fluorescent material plate by the irradiation of the laser light travels in all directions, and the laser light traveling in the fluorescent material is also scattered by the fluorescent material, the intensity per unit area of the emitted light becomes low, and thus eye safety is achieved.
When the laser light scans the surface of the fluorescent material plate, a temperature distribution is generated in the fluorescent material plate. The headlight is exposed to the outside and is also affected by the outside air temperature. For example, a temperature change of −40° C. to +100° C. or higher is expected for the headlight. A mechanical external force such as strain is generated due to the temperature change. The headlight also receives external forces such as vibrations, shocks, etc. from the vehicle body. Due to the influence of these external forces and the like, the fluorescent material plate may not only be detached therefrom, but may also be damaged or broken to generate minute cracks, breakage, and the like.
If a defect such as a minute crack occurs in the fluorescent material plate, there is a possibility that the laser light is directly projected to the outside. In a mechanism for detecting an abnormality of the entire fluorescent material plate such as detachment of the fluorescent material plate, a minute crack or the like cannot be detected, and there may still be a possible risk that eye safety of a person in front of the headlight is impaired.